Are you building a generic caching mechanism? If that the case, then a dedicate cache( with fail-over capability) is not a complete solution. There have enough talks about external cache vs. in process cache on the web, in my experience, people use cache primarily for data from backend DB, but with less tuned configuration, it normally takes < 10 ms to get data directly from DBMS, with highly optimized network and DB cache, it even much better! The only way you can be faster is using in memory cache and maintain a replicated cache map and cache synchronization. Check out JCache stuffs...
I am not saying dedicate service is bad idea, it can be very useful in many situations, it also offer many advantages over in process ones. Caching service can be one usage of it, but in real life external cache need mixed with duplciated cache.
Jboss has very cool distribution management, but in the defense of Weblogic, I will say that archiving what you want in WLS is not that hard. Thought WLS provides no out of box cluster service in a master-slave mode, thought its weighted based load balance can't be applied to RMI, you still can easily plug-in your own Callrouter class, it will provides a list of servers to be used for a particular call, the server in the front of list will always be used unless it's not available.